btnHref.onclick = function () {
  window.location.href = "https://www.imooc.com/";
};
btnAssign.onclick = function () {
  console.log("document.domain:", document.domain);
  // window.location.assign("https://www.imooc.com/");
};
btnReplace.onclick = function () {
  window.location.replace("https://www.imooc.com/");
};
